. Bulletin of the British Museum (Natural History), Geology. . Fig. 4. Pygidia of Dechenella setosa. Group A. (a) Plan view, note constricted axis; (b) Side view; (c) Posterior view. Group B. (d) Plan view, note straight axis; (e) Side view; (f) Posterior view. Both pathological and cicatrized pygidia have been observed in the sample, and it is evident that the species possessed considerable powers of regeneration (PI. 1, fig- 8). IV. AGE OF THE FAUNA Both Calceola sandalina (Linne) and Stringocephalus burtini Defrance have been recorded from the Chercombe Bridge Quarry (Ussher 1913 : 20). Alt
. Bulletin of the British Museum (Natural History), Geology. . Fig. 4. Pygidia of Dechenella setosa. Group A. (a) Plan view, note constricted axis; (b) Side view; (c) Posterior view. Group B. (d) Plan view, note straight axis; (e) Side view; (f) Posterior view. Both pathological and cicatrized pygidia have been observed in the sample, and it is evident that the species possessed considerable powers of regeneration (PI. 1, fig- 8). IV. AGE OF THE FAUNA Both Calceola sandalina (Linne) and Stringocephalus burtini Defrance have been recorded from the Chercombe Bridge Quarry (Ussher 1913 : 20). Although neither has been positively identified during the present investigation, Middleton (1959) has confirmed that the limestones are at least in part of middle Middle Devonian age. Richter (1912) suggested that Dechenella setosa was of Givetian age, and this is supported by the acknowledged Givetian age of all the closely related species. However, Scutellum [Scutellum) flabelliferum (Goldfuss) also occurs in the same horizon; this trilobite is a characteristic Couvinian form. A somewhat stronger case can thus be made out for a Couvinian age, though the presence of Stringocephalus burtini in the same quarry must indicate an horizon near to the Couvinian/Givetian boundary. The limestones of the quarry have so far failed to yield conodonts. V. ECOLOGY AND DISTRIBUTION Since the trilobites are restricted to the black limestone, it seems that sea floor conditions controlled their distribution and that the species was benthonic. The fine-grained bituminous character of the limestone, the presence of pyrite and the great reduction of coral and stromataporoid growth suggest bottom sediments. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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